JP-8 is a kerosene-type military jet fuel derived from petroleum and is being used as the primary fuel for land-based air and ground forces (e.g., aircraft, ground vehicles, and equipment). The US Department of Defense (DOD) is the single largest oil consuming government body in the US, consuming over 90 million barrels of JP-8 in fiscal 2006, which represents about 15% of kerosene-based jet fuel produced by the U.S.
Commercial jet fuel similar to JP-8 in chemical composition is largely consumed by the U.S. commercial (corporate/private) aviation industry with passenger and cargo carriers burning nearly 500 million barrels of jet fuel in 2005. As having already consumed over 80% of its proven oil reserves, the U.S. now imports more than 60% of its oil. It is anticipated that within 20 years the U.S. will be importing from 80% to 90% of its oil. Much of this imported oil is supplied from nations in politically-volatile regions of the world where political instability, human rights abuses, and terrorism are the constant threat to a stable oil supply for the U.S.
Over $250 billion is spent on foreign oil annually, representing a third of the growing US trade deficit and an increasing burden on the US economy. Although the U.S. can continue to increasingly import foreign oil, global oil supplies are not infinite. Even based upon an optimistic estimate of the world oil resource of approximately 2,200-3,900 billion barrels, nearly twice the proven reserve, the world supply of petroleum oil will be depleted within 40 years. Demand for oil by emerging and rapidly growing economies such as in China, India, and South America, is also increasing competition and price volatility for limited global supplies. The severity of potential impacts of oil reduction on U.S. military operations, national security, and the growing economy will depend on how much, how quickly, and how far in advance of this event we are able to provide a wide range of renewable, affordable alternatives to JP-8 and other fossil fuels.
Oil-rich crops and algae are widely regarded as the most promising biological systems for cost-effective, sustainable production of biodiesel particularly for transportation. However, biodiesel produced from current available oil crop-based feedstocks and commercial processes is not suitable as a JP-8 surrogate fuel for military and commercial aviation applications due to its lower energy density and unacceptable cold-flow features. The disqualification of biodiesel as an alternative to JP-8 stems from the fact that the former contains mostly methyl esters of C16 and C18 fatty acids, whereas the latter has the main chemical components of C9 to C14 hydrocarbons. Compared to C9 to C14 hydrocarbons, oxygenated methyl esters of C16 and C18 fatty acids not only decrease energy density of the fuel, but also are responsible for high fuel viscosity, high flash point, and high freezing points (>−50° C.).
Biodiesel can be processed into JP-8 surrogate fuel through thermal, catalytic, and/or enzymatic processes. However, the subsequent secondary processing is neither cost-effective nor energy-efficient and consumes large quantities of fossil fuels with an energy conversion efficiency of 8% to 15%. This results in alternative jet fuel being prohibitively expensive and having unacceptably low energy efficiency. Clearly, transforming algae/plant-based oil or biodiesel into an affordable alternative to petroleum-derived JP-8 has great potential, but this will require significant innovations and improvements to current feedstock production systems and subsequent downstream processes to enhance oil conversion efficiency, while driving production costs down.
One way to increase energy conversion efficiency while reducing production costs of crop oil derived JP-8 surrogate fuel is to introduce certain feedstock oils that may naturally consist of large amounts of medium-chain fatty acids (C10 to C14). The medium-chain fatty acids may require little cracking treatment, which is otherwise required process to break long-chain molecules into shorter ones. Coconut and palm kernel oils have turned out to be the exceptions from common oil crops by containing high concentrations (55˜69% of total fatty acids) of medium-chain (C12 and C14) fatty acids/esters. The world production of coconut oil was about 50 million metric tons in 1999, and the production of palm kernel oil was about 3.8 million tons in 2005. Indonesia, Malaysia, Philippines, and India are the major producers of coconut and palm kernel oils. These oils are mainly used for domestic consumption as food and cooking/frying oil. In the U.S. and other western countries, coconut and palm kernel oils are largely used in the manufacture of margarine and other fat/oil products, as well as in cosmetics, soaps, detergents and shampoos. Although coconut and palm kernel oils are being exploited for production of biodiesel and are considered to be kerosene-based jet fuel substitute, they are unlikely to be used as a major feedstock for jet fuel production due to limited supplies (Shay 1993; Srivastava & Prasad 2000).
An alternative is to make more medium-chain fatty acids through genetic manipulations of oil crops. However, the efforts made thus far with oil-crops have resulted in little commercial significance. This is due mainly to the lack of clear understanding of cellular/subcellular regulatory networks that may provide ‘global’ control over complex biochemical pathways, which may lead to partitioning of photosynthetically-fixed carbon specifically into the formation and accumulation of lipids/oil rather than biosynthesis of protein or carbohydrate. Lack of effective molecular genetic tools and methodologies is another major reason for unsuccessful strain improvement.
Microalgae may be a promising source of feedstock for biofuels because of a) their high lipid/oil contents (40 to 60% of dry weight); b) high specific growth rates (1 to 3 doubling time per day); c) the ability to thrive in saline/brackish water and utilize nutrients (N, P, and CO2) from waste-streams (e.g., wastewater and flue gases from fossil fuel-fired power plants) for growth, and use marginal lands (desert, arid- and semi-arid lands) for wide-scale production all year around; and d) co-production of value-added products (e.g., biopolymers, proteins, polysaccharide, pigments). However, algal oils studied for biofuels so far are rather similar in chemical and physical properties to that of common crop oils, which are enriched with C16 to 18 fatty acids/esters.